Hydrogeomorphic considerations in development planning and stormwater management, central Texas Hill Country, USA

Watershed ordinances in Austin, Texas, USA, are intended to protect streams from stormwater degradation. Their adequacy is being questioned, however, where development is advancing into the hill country northwest and southwest of the city. Detailed investigation into hillslope runoff reveals that several important facts were overlooked in the ordinances, including locally high infiltration rates and drainage basins, which function as partial area systems. As a result, development planning is not taking advantage of the natural mitigation potential of the land. Roads cut across infiltration and moisture retention areas on side slopes, enlarging the partial area system feeding streams with stormflows. In addition, most residential planning is not responsive to the stepped microtopography of hill country drainage basins and the critical scale at which local runoff processes operate. Recommendations include adjusting the scale and configuration of development to conform with local runoff processes and features and taking advantage of the water-absorbing capacities of basin side slopes. The lesson for ordinance writers is that standard models of community stormwater ordinances are not appropriate for all terrains, especially complex ones like the Texas hill country.